This dataset contains data on mixed-species groups of herbivorous reef fish and local species composition in the Lakshadweep Islands, India.

Herbivorous reef fish provide a vital function in reef ecosystems by removing algae and making space available to coral recruits. The high abundance of herbivores in the reefs of the Lakshadweep islands has potentially aided in reef recovery and helped avoid a phase shift to an algal-dominated system, despite most areas having suffered massive coral losses. Mixed-species grouping in herbivores could potentially benefit both the participant species and the reef ecosystem by improving foraging efficiency. We examined the grouping propensity and species richness for three types of herbivore groups after a mass-bleaching event in 2010 and a mass recruitment event in 2015. The species richness and number of parrotfish groups, as well as the grouping propensity of common species, declined starkly across years, indicating that these groups may have formed in response to the mass-bleaching event, slowly diminishing as the reefs recovered. Conversely, large surgeonfish, which varied in richness and propensity across islands and aspect, are likely influenced by local processes. Small surgeonfish only increased in species richness and number in 2015, which may have been in response to the recruitment event. Thus, herbivorous fish may respond differently to local ecosystem perturbations and play different roles in reef recovery.

The Lakshadweep islands, located 200-400 km off the west coast of India, are an archipelago of atolls and small islands, located on the Laccadives-Chagos ridge. This study was carried out within the lagoon and in the reef areas of three of islands within the archipelago, namely Kavaratti, Kadmat, and Agatti. Mixed-species groups were sampled between the months of October-April over the course of three field seasons; 2012-2013, 2013-2014, and 2014-2015. A total of 45 sites were sampled during each year of the study: 15 at each island, with 5 each in the lagoon and in reefs on the eastern and western aspects of the islands. The depth of the sites in the reef ranged from 12-18 meters, and sites in the lagoon ranged between 0.5 to 2 meters. Sampling was conducted using SCUBA in the reef and by snorkelling within the lagoon, between 8 a.m. to 2 p.m.  Groups were sampled using a 60-minute random-walk at the three study islands.  The local species pool of fish was sampled by visual census using timed belt transects.